Control System for and Method of Combining Materials

ABSTRACT

An apparatus and method for combining multiple materials. The multiple materials may include both a major material and one or more minor materials. The major and minor materials are added at transient or steady state flow rates, depending upon a command from a control signal. The actual flow rates track the commanded flow rates, but deviate by an error. The claimed arrangement provides an instantaneous and time-based error believed to be unobtainable in the prior art.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 11/895,421,filed Aug. 24, 2007, which is a continuation-in-part of U.S. patentapplication Ser. Nos. 11/217,273 and 11/217,802, both filed Sep. 1,2005.

FIELD OF THE INVENTION

The present invention relates to a method and control system forcombining materials.

BACKGROUND OF THE INVENTION

Many methods are known in the art for combining fluid materials.Typically, the materials are combined upstream of a mix tank. Suchmaterials are then jointly added to the mix tank and stirred until ahomogenous blend is achieved. Further processing steps downstream of theconfluence region may include the addition of more material(s), theaddition or removal of energy, such as thermal energy, etc.

Additionally or alternatively, such materials can be mixed in a dynamicmix tank using mechanical agitation and/or alternative forms ofagitation, such as ultrasonic vibration. The combined materials, orblend, may then be transported downstream and become an intermediate forfurther processing. Alternatively, these materials may be added to acontainer for ultimate sale or use.

The prior art methods and systems have several disadvantages. If such amix tank is used, it can require considerable energy to achieve thedesired mixing. If one desires to change the formulation, or even theminor materials, this change usually entails cleaning the entire tankand associated system. Cleaning the entire system can be time-consumingand laborious. Then new materials are added and the process beginsagain. Considerable waste of time and materials can occur.

Transients from no production or low rate production to full productionrates are inevitable when changes between different products occur, etc.It is generally desirable that such a transient be over and steady stateoperation resume as quickly as possible. This is because one typicallydesires reaching steady state production rates as soon as reasonablypracticable. Furthermore, product manufactured out of specificationduring transients may be wasted. If one were to accept a slowertransient, then it is likely greater accuracy in the productsmanufactured during the transient can occur and less product may bewasted by having a slower transient. Thus a tradeoff is present in theart.

Often, the speed in which a system and respond to transients is limitedby the hardware. For example, a flow meter which is intended to provideactual flow rate at a particular point in time may not follow and/orindicate a change in flow rate as quickly as one would like for the rateof change of the transient. For example, valves which provide flowcontrol and ultimately the rate of material addition may not respond asquickly as one would desire. Furthermore, different sizes of valves,different operators used in conjunction with the valves, and even valvesfrom different manufacturers may respond at different rates once acommand signal is received. Yet further, the same valve may respond atdifferent rates over different portions of the open/close cycle.

Accordingly, what is needed is an apparatus, and process of using suchapparatus, which allows for quickly changing the formulation of a blend,accurately follows transients, minimizes wasted materials, and rapidlyprovides for homogeneity in the blend. Unless otherwise stated, alltimes expressed herein are in seconds, proportions and percentagesherein are based on volume. Optionally, the invention may useproportions and percentages based on mass.

SUMMARY OF THE INVENTION

The invention comprises a method and apparatus for blending together twoor more materials in a predetermined proportion. The materials may becombined at various flow rates with various ramps therebetween, whilemaintaining the predetermined proportion within a relatively tight errorband, considering either the instantaneous error at a point in time orthe cumulative error over a period of time.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an exemplary system according to thepresent invention, shown partially in cutaway and providing for eightminor materials.

FIG. 2 is an instantaneous vertical sectional view of an exemplarysystem according to the present invention, schematically pumps forsupplying the minor materials to the confluence region and acircumferential clamp therearound.

FIG. 3 is a graph showing the performance curve of an illustrativesystem according to the prior art for a command signal having a stepinput.

FIG. 4 is a graph showing a transient response curve of an exemplarysystem according to the present invention for a step input, as comparedto an idealized theoretical response of the prior art for the same stepinput.

FIG. 5 is a graph of transient response curves of a system for a 0.2second ramp input showing the command signal and certain processvariables for one major and two minor materials.

FIG. 6 is an enlarged graph of the transient response curve of one ofthe minor materials in FIG. 5.

FIG. 7 is a graph showing the instantaneous error of the system of FIG.4.

FIG. 8 is a graph showing the cumulative error of the system of FIG. 4.

FIG. 9 is a schematic diagram of a flow rate feedback control system,according to the prior art.

FIG. 10 is an exemplary schematic diagram of a motor position feedbackcontrol system usable with the present invention, showing optionalcomponents in dashed.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1-2, the invention comprises an apparatus 10 andprocess for combining, blending or mixing two or more materials.Combining refers to adding materials together with or withoutsubstantial mixing towards achieving homogeneity. Mixing and blendinginterchangeably refer to combining and further achieving a relativelygreater degree of homogeneity thereafter.

The resulting combination of materials may be disposed in a container(not shown). The container may be insertable into and removable from theapparatus 10. The apparatus 10 comprises apparatus 10 hardware foradding at least one major or first material to the container and foradding at least one minor or second through nth materials to thecontainer. The apparatus 10 for adding the major material(s) and minormaterial(s) provides for some or all of these materials to come togetherin a confluence region 12. The confluence region 12 is the region orpoint where the major material(s) and at least one, and likely each, ofthe minor material(s) initially come into contacting relationship withone another and is where mixing may occur. Mixing of the majormaterial(s) and minor material(s) may occur at the confluence region 12,downstream thereof, or both.

The confluence region 12 may comprise one or more inlets 14A, which maybe referred to as a major material inlet 14A, for supplying one or moremajor materials, and at least one inlet 14I, each of which may bereferred to as a minor material inlet 14I, for supplying one or moreminor materials. The confluence region 12 may further comprise at leastone common outlet 16 for discharging the major material(s) and minormaterial(s) from the confluence region 12, and optionally directly intothe container or optionally to the container after further processing.It is understood that after the materials leave the confluence region 12through the common outlet 16, a single container may be filled or pluralcontainers having equal or unequal volumes and flow rates thereinto maybe filled in parallel.

The apparatus 10 for supplying the minor material(s) may comprise one ormore inlet tube(s) 14I inserted into the apparatus 10 for supplying theminor material(s) directly to the confluence region 12. Each minormaterial may have a dedicated inlet tube 14I or, alternatively, pluralminor materials may be inserted through a single inlet tube 14I. Ofcourse, if desired, the same minor material may be added through morethan one inlet tube 14I, in various combinations of like or differentmaterials, quantities, feed rates, flow rates, concentrations,temperatures, etc.

The inlet 14I for each of the minor materials terminates at an inletdischarge 18. The inlet discharges 18 may lie in a common plane, asshown. The inlet discharge 18 defines the beginning of the confluenceregions 12, as noted above. The inlet discharge 18 is the point a minormaterial leaves a respective inlet 14I and enters the confluence region12. The inlet discharge 18 may be closely juxtaposed with an inlinemixer, so that mixing of the materials occurs almost immediately in theconfluence region 12.

While apparatus 10 having eight inlet tubes 14I, each equally spacedfrom the other, are illustrated, one of skill will recognize theinvention as not so limited. More or less inlet tubes 14I may beprovided and be equally or unequally spaced circumferentially, radially,and/or longitudinally. Further, the inlet tubes 14I may have equal orunequal cross sectional areas, shapes, lengths and flow ratestherethrough. The minor materials may be supplied to the inlet tubes 14Ifrom one or more common sources or from different sources.

If desired, the volume of the inlet tubes 14I for the minor materialsmay be relatively small relative to the total volume of the entireapparatus 10. This relative sizing provides the benefit that lesshysteresis in the system might occur, due to the small volume of theinlet tubes 14I between the pump 20, and the confluence region 12.

The apparatus 10 may comprise a plurality of supply lines for the minormaterials. Each supply line may extend from the source of at least onemajor material or at least one minor material to a respective inletdischarge 18 within the confluence region 12.

The inlet discharge 18 may occur at the distal end of an inlet tube 14I.Each supply line thereby defines a volume from its respective materialsupply to its respective discharge within the confluence region 12. Theat least on supply for adding at least one major material subtends afirst volume extends from that material source to the common plane wherethe inlet discharges 18 occur. Each supply for adding each of said minormaterials subtends a sub-volume. The sub-volumes are combined to yield asecond volume. The first volume and the second volume are summed toyield a total volume. The second volume may comprise less than 20percent, less than 10 percent, less than 5 percent or less than 3percent of the total volume.

The first material may be injected into the confluence region 12 at afirst velocity. The second through Nth materials may be injected intothe confluence region 12 at a second velocity, a third velocity, . . .up to N velocities for N minor materials. The second through Nthvelocities may be matched to, substantially the same as, or may beslightly different than the first velocity and each other. One or moreof the minor materials may generally correspond with or be matched inflow velocity at the time of entry into the confluence region 12 to thevelocity of the at least one major material(s) at that samecross-section of the confluence region 12. In one embodiment of theinvention, any or all of the second through Nth velocities of the minormaterials may be within ±50 percent, and may even be more closelymatched to within ±25 percent, and may even be more closely matched to±5 percent of the first velocity of the major material(s). Thisarrangement allows the minor materials to enter the flow as a continuousstream, without dribbling, and thereby promote better mixing. Thedischarge speed of the minor material into the flow stream is determinedby a combination of the discharge orifice (if any) and the output of thepump 20 supplying that minor material. In a degenerate case, the firstvelocity may be identically matched to any or all of the second throughNth velocities.

If desired the apparatus 10 and method including the present inventionmay utilize plural confluence regions 12. The plural confluence regions12 may be disposed in series, in parallel, or a combination thereof. Theplural confluence regions 12 may be identical or different in any or allof their major materials, minor materials, proportions, flow rates,command signals, etc. Certain plural confluence regions 12 may be usedto premix minor materials, major materials, or any combination thereofto be mixed with other materials in later—occurring in confluenceregions 12.

The container may be the final receptacle for the combination of themajor and minor materials after they are blended together and leave theconfluence region 12. The container may be ultimately shipped and soldto the consumer, or may be used for transport and storage of the blendof major materials and minor materials as an intermediate.

The container may be moved into and out of the apparatus 10 under itsown power, as occurs with a tanker truck container, may be moved by theapparatus 10 itself, or by an outside motive force. In a degeneratecase, all of the minor materials are added to one major material at thesame point, thereby defining the beginning of the confluence region 12.The end of the confluence region 12 is defined as the common outlet 16therefrom. In a degenerate case, the common outlet 16 may be intoatmospheric pressure conditions, such as into a container filled withair, into a vacuum, such as an evacuated container, or even into apressurized container. The blend or other combination of materials maybe held above atmospheric pressure from the confluence region 12 to thepoint of discharge into the container.

The container may be of any suitable size, geometry, configuration,number, etc. The volume of the container may range from a few cubiccentimeters to at least the size of a railroad tanker. The container maybe provided with a frangible or resealable closure as are well known inthe art, and be made of any material suitable for containing thematerials combined according to the present invention.

The end of the confluence region 12 can also be defined as that point atwhich substantial homogeneity is obtained and additional intermixing ofthe materials is insubstantial. Such a point may occur prior todischarge into a container. The length of the confluence region 12 isdefined as the distance from the beginning of the confluence region 12to the aforementioned common outlet 16. The volume of the confluenceregion 12 is the length multiplied by the cross-sectional area of theconfluence region 12 therein. The length of the confluence region 12 maybe relatively short compared to the inlet tubes 14I and other geometriesin the system.

While a confluence region 12 of constant cross section is shown, onewill realize the invention is not so limited. The invention may be ofvariable cross section, such as convergent, divergent, barrel-shapedVenturi-shaped, etc.

As used herein, a major material is the largest single material in thefinal combination and may refer to any one material which comprises morethan 33 percent, and, in another embodiment, even more than 50 percent,and may even comprise more than 67 percent of the total composition.Equal volumes for plural major and minor materials are contemplatedherein. In contrast, a minor material is any one material which maycomprise less than or equal to 50 percent, in another embodiment 10percent, in another embodiment less than 5 percent, and in still anotherembodiment less than 1 percent of the total composition. The inventionalso contemplates plural materials in equal and/or relatively equalproportions and/or flow rates.

The apparatus 10 for supplying the major material may comprise a pipe,conduit, open channel, or any other suitable apparatus 10 through whichthe materials may flow. While a round pipe is illustrated, the inventionis not so limited. Any desired cross section, constant or variable, maybe utilized.

The apparatus 10 and method described and claimed herein do not requirea dynamic mix tank. As used herein, a mix tank refers to tanks, vats,vessels and reactors and is inclusive of the batch and continuous stirsystems which use an impeller, jet mixing nozzle, a recirculating loop,gas percolation, or similar means of agitation to combine materialstherein. It can be difficult to quickly and accurately follow andachieve desired transient flow rates using a dynamic mix tank. This isbecause flow stagnation and interruption may occur while materials arebeing combined in a dynamic mix tank. Different proportions of flowrates can occur and prevent the desired product formulation from beingachieved. If the desired formulation is not achieved, product is wasted.Furthermore, the residence time often necessary to achieve mixing andaxial dispersion of the materials requires energy and may be difficultto achieve with multiple additions of minor materials.

The apparatus 10 described and claimed herein may utilize an inlinemixer. As used herein an inline mixer refers to a mixing device whichdoes not impute macro-scale flow stagnation, or prevent a continuousflow through portion of the apparatus 10 having the inline mixer fromoccurring. One non-limiting type of inline mixer is, for example, anultrasonic or cavitation type mixer. One such system is a Sonolatorhomogenizing system available from Sonic Corporation of Stratford, Conn.Another non-limiting type of inline mixer is a static mixer as known inthe art and disclosed in U.S. Pat. No. 6,186,193 B1, issued Feb. 13,2001 to Phallen et al. and in commonly assigned U.S. Pat. Nos. 6,550,960B2, issued Apr. 22, 2003 to Catalfamo et al.; 6,740,281 B2, issued May25, 2004 to Pinyayev et al.; 6,743,006 B2, issued Jun. 1, 2004 to Jafferet al.; and 6,793,192 B2, issued Sep. 21, 2004 to Verbrugge. Further, ifdesired, static mixers or other inline mixers may be disposed in or withone or more of the inlet tubes 14A or upstream of the confluence region12. Additionally, surge tanks may be used to provide more constant flowfor materials combined by the apparatus 10 and method described andclaimed herein. Additionally or alternatively a Zanker plate may beutilized.

The major and/or minor material(s) may comprise a fluid, typically aliquid, although gaseous major and minor materials are contemplated. Themajor and/or minor material(s) may include, but are not limited tosuspensions, emulsions, slurries, pastes, gels, aqueous and nonaqueousmaterials, pure materials, blends of materials, etc.

Optionally, at least one of the major material(s) and one or more of theminor material(s) may comprise a solid, such as a granular orparticulate substance. Granular or particulate materials may be added inany known fashion, including but not limited to that disclosed incommonly assigned U.S. Pat. No. 6,712,496 B2, issued Mar. 30, 2004 toKressin et al.

While the invention is described below in non-limiting, exemplary termsof pumps 20 and servomotors, the invention is not so limited and may useany motive force or similar means for supplying the major and minormaterials. A used herein motive force refers to any force used toprovide energy which, in turn, is used to supply materials to theconfluence region 12 and may include, without limitation, electricmotors, gravity feeds, manual feeds, hydraulic feeds, pneumatic feeds,etc.

The at least one major material(s) and/or at least one minor material(s)may be supplied from a hopper, tank, reservoir, pump 20, such as apositive displacement pump 20, or other supply or source to the pipe, orother supply devices, as are known in the art and provide the desiredaccuracy for dosing such materials. The major material(s) and/or minormaterial(s) may be supplied via a pump 20, auger feed, or any othersuitable means.

The apparatus 10 for providing the major and/or minor materials maycomprise a plurality of positive displacement pumps 20. Each pump 20 maybe driven by an associated motor, such as an AC motor or a servomotor.Each servomotor may be dedicated to a single pump 20 or optionally maydrive plural pumps 20. This arrangement eliminates the necessity ofhaving flow control valves, flow meters and associated flow controlfeedback loops as are used in the prior art.

As used herein, a flow control valve refers to a valve quantitativelyused to allow a specific quantity or flow rate of material to passthereby and is used to modulate actual flow rate. A flow control valvedoes not include an on-off valve which allows the process according tothe present invention to qualitatively start or stop.

Referring to FIG. 9, an illustrative flow control feedback loopaccording to the prior art is illustrated. A flow control feedback loopcompares a flow rate set point, or command signal, to a measured flowrate. A subtraction is performed to determine an error. The error, inturn, is used to adjust or correct the velocity drive control. Thevelocity drive control is associated with a motor operatively connectedto the pump 20 from which the actual flow rate is measured. This systemhas the disadvantage that the system response may be dictated by andconstrained by the accuracy and response time of the flow meter.

Referring to FIG. 10, a nonlimiting, exemplary motor control loopaccording to the present invention, is shown. Such a motor control loopmay or may not comprise at least one of a feedforward loop and/orfeedback loop, so long as the control system does not have zero gain inthe position control or velocity control if the appropriate feedforwardloops are not utilized.

If desired, the motor control loop may comprise nested control loops.The innermost of these loops may be a torque control feedback loop,which is shown as a single box scaling both torque and current. A torquecommand is input to the torque control. The torque control converts thetorque command to an equivalent current command, which is input to thecurrent controller for the motor. The current controller, in turn,provides a current feedback signal to the current control. However atorque control may be utilized, recognizing there it is a mathematicalrelationship between torque and current, which may be determined using ascaler. The torque control loop may be surrounded by a velocity controlfeedback loop, which, in turn, may be surrounded by a position controlfeedback loop. The velocity feedback control loop, the position feedbackcontrol loop and/or a feedforward path for velocity and/or accelerationare optional features for the present invention. The velocity andacceleration feed forward loop may utilize respective gains K_(vff) andK_(aff), as shown.

The derivative of the motor position with respect to time may be takento yield motor velocity, or oppositely, the velocity feedback may beintegrated with respect to time to yield motor position. The motorposition control loop may use a motor position command signal andcompare this set point or command signal to the motor position feedbackto calculate position error. A velocity setpoint can be derived from theposition error using the position controller.

The velocity setpoint may be compared to actual motor velocity to alsodetermine a velocity error. This velocity error may be used to adjustthe actual velocity of the motor, using known techniques. The motorvelocity may then be correlated to pump 20 output, as is known in theart.

Optionally, the position setpoint may have its derivative taken withrespect to time, to yield a feedforward velocity. The feedforwardvelocity may be input to the velocity setpoint summer and used inconjunction with the output of the position loop control to generate avelocity loop command signal. The feedforward velocity may also be usedwithout taking into account the position loop control signal, in orderto generate the velocity loop command signal. Optionally, thefeedforward velocity may have its derivative taken to yield afeedforward acceleration. Likewise, the feedforward acceleration may beused in conjunction with, or without, the output of the velocity loopcontroller to determine the acceleration profile of the motor, which isproportional to the torque command signal issued to the motor.

The setpoints of the major and minor materials may be generated as afraction or percentage of a master volumetric setpoint or commandsignal. The master volumetric setpoint may be defined in terms of totalflow volume, flow rates, and/or time rate of change of flow rates.

While the foregoing discussion is directed to a motor control loop basedon motor position, one of the skill will recognize the invention is notso limited. The motor control loop may be based on motor position, motorvelocity, motor acceleration, motor current, motor voltage, torque etc.Such a control system and method may be used to define a master setpointin terms of torque/current, position, velocity, and/or acceleration,providing there is a direct relationship between flow andtorque/current/position/velocity/acceleration, as occurs with thepresent invention. The major and minor material setpoints may be inputto the individual motive force systems as a command position and/orvelocity and/or torque setpoint.

The motor position setpoint, or command signal, may be sent to one ormore servomotors. According to the present invention, all of the majormaterials and minor materials may be driven in unison through suchservomotors, each of which may be coupled to one or more pumps 20.Instead of or in addition to the pump 20/servomotor combination, one ofordinary skill may use a variable frequency drive to vary the voltagesupplied to an AC motor-driven pump 20. Alternatively, or additionally,pump 20 output can be changed using various other means, as are known inthe art. For example, to vary pump 20 output for a given motor, onecould use a mechanical variable speed/adjustable speed drive, amulti-speed transmission/gearbox, and/or a hydraulic adjustable speeddrive.

This arrangement provides the benefit that the flow rates of some or allof the major materials and minor materials can be ramped up or down inunison without requiring a common drive or flow control valves,providing greater fidelity to the desired formulation of the final blendof all materials. Thus, if one desires to have a step change, a rampchange either up or down, or even a start/stop in one or more flowrates, this transient can be accommodated more quickly than according tothe prior art known to the inventors. Thus, the proportion of major andminor materials remains within a relatively tight tolerance of thedesired formulation without unduly disrupting or unduly decreasing aflow rate usable for production quantities.

As noted above, this arrangement provides the benefit that it is notnecessary to have a control loop directly monitoring flow rates.Instead, the flow rates for the major and minor materials may bedetermined by knowledge of the pump 20 characteristics for a given fluidviscosity, pump 20 type, and inlet/outlet pressure differential. Basedon a desired flowrate, pump 20 compensation algorithms may be used toachieve accurate flow rate delivery without requiring direct flowmeasurement. Direct flow measurement may introduce delays andinaccuracies during high-speed transient response due to limitationsinherent in the instrumentation, system hysteresis, etc.

The pump 20 may be driven to its desired rotational speed depending uponpump 20 capacity, including any motor or pump 20 slip factor to accountfor the pump 20 operating at less than 100 percent efficiency. Ifdesired, the apparatus 10 and method according to the present inventionmay monitor torque, position, velocity and/or acceleration of the motorshaft.

Thus, an apparatus 10 and method according to the present inventionmight not have a flow feedback loop to compensate for variations in flowrate or even a flow meter to monitor the addition and/or rate ofaddition of the individual major or minor materials, for example, asthey are added to the confluence region 12. Such a control systemprovides a relatively high degree of fidelity to the desired, i.e.commanded, response.

The apparatus 10 and method claimed herein may be controlled by acommand signal as is known in the art. The command signal may beconsidered to be a dynamic setpoint, and is the target rate of materialaddition for each material at a given point in time. The command signalmay be sent from a computer, such as a PLC. The signal from the PLC maybe sent to a motor drive system. The PLC and drive system may beinternal or external to the system under consideration.

If desired, each motor may have a dedicated drive controller. Thecommand signal(s) is/are sent from the computer to the drive controllerand then to the motor, which may be a servomotor. Of course, one ofskill will recognize that other apparatus 10 and means for adding thematerials may be utilized and the command signal sent from thecontroller to such apparatus 10 or means of material addition. Uponreceipt of the command signal, the servomotor accelerates or deceleratesto the specified rotational speed for its associated pump 20 or otherapparatus 10 or means of material addition. The rate of materialaddition is thereby controlled from the command signal.

Two types of tracking error may be considered with the presentinvention. Tracking error is the difference between the value of acommand signal and a process variable. The first is the instantaneoustracking error given in volume of material transferred per unit time.The instantaneous error measures the difference between any processvariable and the command signal at a specific point in time.

The second tracking error one may consider the cumulative error. Thecumulative error is the sum of each instantaneous error for eachmaterial under consideration throughout a specific period of time and ismeasured in volume. The period of time under consideration will dependupon the length of the transient.

Referring to FIGS. 3 and 4, the tracking error shown is the differencebetween the command signal and a feedback process variable. In FIG. 3,the particular feedback process variable is the actual flowrate measuredby a flowmeter for purposes of benchmarking. However, according to thepresent invention, a flowmeter is not necessary for production ofmaterial combinations, mixtures or blends.

FIG. 3 particularly shows the performance of one system according to theprior art. This system had a pipe with a nominal diameter of 5.1 cm.Flow was controlled by a flow control ball valve available from FisherControls, a division of Emerson of St. Louis, Mo. The valve wascontrolled by an Allen-Bradley ControLogix 1756-5550 controller. Thecontroller relayed signals to the control valve based upon measured flowrate. Flow rate was measured by a Micro Motion CMF100 ELITE mass flowmeter with an RFT 9739 transmitter, also available from Emerson. Thesystem used water at a pressure of approximately 10 bar in response to astep input. Examination of FIG. 3 shows that the system tookapproximately 40 seconds to reach steady state conditions.

FIG. 4 shows the ideal theoretical response to a step input using acontrol valve. The command signal shows a step input. The response iscalculated according to the formula: g(t)=1−e^(−t/τ) using a one secondtime constant (τ). Even under such favorable theoretical conditions,FIG. 4 shows that it may take approximately four time constants, andtherefore four seconds in this example, to reach steady stateconditions.

FIG. 4 also shows that for a step input, steady state conditionsaccording to the present invention may be reached in less than 0.1seconds. The system according to the present invention in FIG. 4utilized a command signal from an Allen Bradley ControlLogix 1756-L61processor communicating via a Sercos 1756-M16SE communication card to anAllen Bradley Kinetix 6000 drive system for the minor material. Theminor material, a dye solution, was supplied by a Zenith C-9000 pumpavailable from the Colfax Pump Group of Monroe, N.C. and driven by anAllen Bradley MPF-B330P servomotor. The servomotor had a dedicatedSercos Rack K6000 drive. The servo motor and the pump 20 were connectedthrough an Alpha Gear SP+ drive available from Alpha Gear of Alpha GearDrives, Inc. of Elk Grove Village, Ill.

As shown in FIGS. 3-4, in the prior art, low tracking error andrelatively constant proportions of materials were difficult to achievewith a step change or with a sharp ramp change. This is because not allof the valves, actuators, etc., could respond simultaneously, insynchronization, and in the same proportion during these rapid changeconditions. However, with the present invention and the absence ofvalves, particularly flow control valves, dynamic mix tanks, theassociated hysteresis, etc., greater fidelity of response to the commandsignal can be achieved.

One transient which may be considered is from the start of flow, or thestart of a change in flow rate command, to the point at which steadystate operation is achieved. Such a transient is shown in FIGS. 5-6.FIGS. 5-6 were generated with a system according to the presentinvention. This system had a horizontally disposed, 5.1 cm diameterconfluence region 12 with a constant cross section. The confluenceregion 12 had eight inlets 14I, each with an inner diameter of 3 mm,disposed on a diameter of 1.5 cm as shown in FIGS. 1-2, although onlytwo inlets 14I were utilized for this example.

The major material comprised a liquid soap mixture. The first and secondminor materials comprised two different dye solutions. The majormaterial, first minor material and second minor material were set to thedesired proportions of 98.75, 0.75, and 0.5 percent respectively. Theactual command signal issued to the servomotor control may be adjustedin accordance with known pump 20 compensation algorithms to account forthe common pump 20 inefficiencies and irregularities.

The major material was supplied by a Waukesha UII-060 pump availablefrom SPX Corp. of Delavan, Wis. and driven by an Allen Bradley MPF-B540Kservomotor. Each minor material was supplied by a Zenith C-9000 pumpavailable from the Colfax Pump Group of Monroe, N.C. and driven by anAllen Bradley MPF-B330P servomotor. Each servomotor had a dedicatedSercos Rack K6000 drive and was connected through an Alpha Gear SP+drive available from Alpha Gear of Alpha Gear Drives, Inc. of Elk GroveVillage, Ill. The system was controlled by an Allen Bradley ControlLogix1756-L61 processor communicating via a Sercos 1756-M16SE communicationcard to an Allen Bradley Ultra 3000 or Allen Bradley Kinetix 6000 drivesystem for the major and minor materials, respectively.

A fourteen element SMX static mixer available from Sulzer was disposedwithin approximately one mm of the start of the confluence region 12. Atwelve element SMX static mixer was disposed approximately 46 cmdownstream of the first static mixer. The materials were considered tobe adequately mixed after the second static mixer.

As shown by FIGS. 5-6 the present invention may be used with transientshaving various increasing flow rates, various decreasing flow rates, orwith steady state operation at various constant rates. The curveillustrated in FIG. 5 can be divided into three generally distinctsegments. The first segment of the curve is the ramp-up where flow ratesof each of the materials increases from zero to a predetermined valuefor each material. The second portion of the curve is the steady stateflow, wherein the flow rates are maintained relatively constant and maybe usable for production quantities. The third portion of the curveshows the ramp-down from the steady state flow rate to a lesser flowrate. The lesser flow rate may be zero, in the degenerate case, or itmay be a flow rate which is simply less than that shown in the otherportions of the curve. Throughout all three portions of these curves theproportion of each material to the total of the blend of all materialsin the feed is maintained substantially constant.

In one embodiment the command signal may be for a transient to go from ano flow or zero flow signal to a signal of 100 percent of full scaleflow in a single transient although steady state flow rates of less than100 percent may be utilized. The transient may be commanded to occur innot more than 2 seconds, not more than one second, not more thanone-half second or less. During such a transient, according the presentinvention, each major or minor material, i.e. first, second third . . .nth material, may remain within ±10 percent, 5 percent, 3 percent ormeasured full scale flow throughout the transient. The percentage may bebased on the instantaneous error, described below.

Of course, one of ordinary skill will realize the invention is notlimited to transients with only three different flow rates. Thetransition from a first steady state flow may be to a greater or lessersteady state flow rate. Multiple transitions, both increasing anddecreasing in any combination, pattern, of equal or unequal timeperiods, ramps, etc., may be utilized as desired.

According to the present invention, the at least one first material andat least one second material occur in a generally constant proportion,i.e., constant flow relative rates into the confluence region 12throughout the steady state operating period. Likewise, thesubstantially constant proportion is maintained throughout thetransitional flow rate periods as well. The substantially constantproportion is maintained both as flow rates increase and decrease, solong as the flow rate is greater than a near zero, nontrivial value.

While a first order, linear rate of change throughout the transitionregions is illustrated in FIGS. 5-6, the invention is not so limited. Asecond order, third order, etc., rate of change may also be utilized, solong as the substantially constant proportion is maintained. It is onlynecessary that the pumps 20, or other motive forces, be controlled insuch a way that generally constant proportionality is maintained. Whileconstant proportion may be more readily envisioned, and easier toexecute and program utilizing a linear rate of change, one of skill willrecognize other options are available to maintain the constantproportion throughout the transitions.

Referring back to the systems of FIGS. 3-4 and as illustrated by Table1, which tabulates the data illustrated in FIG. 4, the instantaneouserror according to the prior art decreases throughout the duration ofthe transient. However, this error never reaches the relatively lowvalue of the present invention within the 5 second time periodillustrated in Table 1. Table 1 also illustrates the cumulative errorfor both the prior art and present invention systems.

TABLE 1 Time in seconds from start of command signal step. Commandsignal issued at T = 1 second. Tracking Error 0.1 sec. 0.25 sec. 0.50sec. 1 sec. 5 sec. INSTANTANEOUS ERROR (volume/sec) Prior Art 0.9050.779 0.607 0.369 0.009 Present Invention 0.002 0.002 0.002 0.002 0.002CUMULATIVE ERROR (volume) Prior Art 0.089 0.215 0.386 0.624 0.990Present Invention 0.006 0.006 0.006 0.007 0.015

FIG. 7 illustrates that the instantaneous error can be approximated bythe first order exponential equation:

IE=A*M*exp(−t/τ)

Where

-   -   IE is the instantaneous error in volume per unit time, and    -   A is the magnitude of the setpoint change, normalized to unity        for the present invention,    -   M is a coefficient of the amplitude which reduces the value of        the amplitude from the normalized unity setpoint magnitude to        any value from 0 to 1, or from 0.1 to 1, or from 0.2 to 1 or        from 0.3 to 1 or from 0.4 to 1 or from 0.5 to 1, as desired,    -   t is the instantaneous time in seconds,    -   τ is the time constant in seconds.

This approximation is particularly suitable for prior art transientslasting up to 1 second, 2 seconds, 3 seconds, 4 seconds and even 5seconds. Illustrative, non-limiting combinations of the coefficient,time constant and time period under consideration are set forth in Table2.

TABLE 2 M Tau t (sec) 0.5 1.0 0 − 0.5 * τ 0.5 0.75 0 − 1.33 * τ 0 − 1 *τ 0 − 0.5 * τ 0.5 0.5 0 − 3 * τ 0 − 2 * τ 0 − 1 * τ 0.5 0.25 0 − 8 * τ 0− 4 * τ 0 − 2 * τ 0.25 1.0 0 − 1.5 * τ 0 − 1 * τ 0.25 0.75 0 − 2 * τ 0 −1 * τ 0.25 0.5 0 − 3 * τ 0 − 1.5 * τ 0.25 0.25 0 − 4 * τ 0 − 2 * τ

FIG. 7 further shows that the present invention may achieve aninstantaneous error given by the following exemplary inequalities,although any of the combinations set forth in Table 2 or otherwise maybe utilized.

IE<A*M*exp(−t/τ) for values of M=0.5, τ=1, evaluated from time t=0 to0.5*τ or more particularly

IE<A*M*exp(−t/τ) for values of M=0.5, τ=0.5, evaluated for t from 0 to3.0*τ or more particularly

IE<A*M*exp(−t/τ) for values of M=0.25, τ=1.0, evaluated for t from 0 to1.5*τ.

The instantaneous error can be integrated over a desired time period toyield a cumulative error for that period according to the formula

 ^(t₂)CE = ∫_(t₁)IE (t)

Where

-   -   CE is the cumulative error,    -   t₁ is the starting time and set to 0 for the degenerate case,        and    -   t₂ is the end of the time period under consideration.

FIG. 8 illustrates that the cumulative error according to the prior artcan be approximated by the equation

CE _(k)=(0.5*(IE _(k-1) +IE _(k))*ΔT)+CE _(k-1)

Where

-   -   CE is the cumulative error in volume,    -   k is the index for the specific discrete time period,    -   ΔT is the discrete time sampling and period, in seconds, and    -   IE remains as previously defined.

However, one of skill will recognize that the instantaneous errorapproaches zero as time continues towards steady state flow. Since thecumulative error is dependent upon instantaneous error, the cumulativeerror will not significantly increase as the instantaneous errorapproaches zero. One of ordinary skill will recognize that anycombination of values set forth in Table 2 may be utilized with thepresent invention, so that the invention is not limited to the aboveinequalities for instantaneous error or associated cumulative error.

If desired, one may utilize a piston pump with the present invention. Apiston pump may provide more versatility with certain fluids which maybe used in conjunction with the present invention, and also has apulsating output which provides repeating fluctuations in the flow rate.If desired, one may program the servomotor to have a negativesuperposition with the actual pump output so that the fluctuations aredampened by using camming of the motor, as is known in the art. Thisprovides the advantage that no dampener is necessary in the systemdownstream of the piston pump. The dampener may add hysteresis or otherundesirable affects which are avoided according to the presentinvention.

An alternative embodiment of the invention is presented. In thisembodiment, a small portion, which may be a minority portion, of theproduct stream is diverted. The diverted portion of the product may haveall of the materials of the final product as desired. Alternatively, thediverted minority portion may be missing one or more materials.

The diverted minority portion of the product stream may have at leastone material added using the apparatus 10 and method disclosed herein.The minor material may be added to the diverted stream immediatelyupstream of an ultrasonic horn, static mixer, etc. This portion of thestream is then usable as an intermediate or final product. This minorityportion, having thus been completed, is then discharged into thecontainer for ultimate use.

The majority portion of the stream may continue through the processunabated, without the further addition of a minor material, and withoutdiversion. Alternatively, additional minor materials may be added to themajor portion of the product stream. The major portion of the productstream is then sent to a container for ultimate use, as disclosed above.

This arrangement provides the benefit that parallel manufacture of amajor product and a minor product may be simultaneously accomplished.For example, the major portion of the product may comprise a first die,perfume, additive, etc. A less popular or less often used minor portionof the product stream may be diverted and have a second die, perfume, orother additive included in the final product. Alternatively, thisarrangement provides the benefit that the major portion of the productmay be produced without a particular dye, perfume, additive, etc., whilea desired dye, perfume, or other additive is included in the divertedstream of the minority product, or vice versa. This arrangement providesthe benefit that both products may be produced in any desired proportionwithout costly shutdown, cleaning, etc.

Of course, one of skill will recognize that more than a single minorityproduct stream may be diverted. Plural minority streams may be diverted,each producing a relatively small quantity of the final product with orwithout specific and other additives. This arrangement providesflexibility in the manufacturing process for producing a large ormajority first quantity of a blend of materials and one or morerelatively small, even very small, minority quantities of materials, allwithout shutting down and recleaning the apparatus 10 and associatedsystems.

The dimensions and values disclosed herein are not to be understood asbeing strictly limited to the exact numerical values recited. Instead,unless otherwise specified, each such dimension is intended to mean boththe recited value and a functionally equivalent range surrounding thatvalue. For example, a dimension disclosed as “40 mm” is intended to mean“about 40 mm.”

All documents cited in the Detailed Description of the Invention are, inrelevant part, incorporated herein by reference; the citation of anydocument is not to be construed as an admission that it is prior artwith respect to the present invention. To the extent that any meaning ordefinition of a term in this written document conflicts with any meaningor definition of the term in a document incorporated by reference, themeaning or definition assigned to the term in this written documentshall govern.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention. It is thereforeintended to cover in the appended claims all such changes andmodifications that are within the scope of this invention.

1. An apparatus for combining at least two materials together, said atleast two materials comprising a major material and at least one minormaterial, said apparatus comprising a confluence region where said atleast two materials come together, wherein said apparatus is configuredto provide said materials so that said materials undergo a transientflow rate whereby the amount of said materials blended per unit time isvaried either to be greater than or less than a prior rate of blendingsaid materials, whereby said transient flow rate produces aninstantaneous error and a cumulative error between a command signal sentfrom a computer, said command signal having a setpoint which is changedat time T=0 and a measured flow rate, said instantaneous error being notmore than:IE<A*M*exp(−t/τ) Where IE is the instantaneous error in volume per unittime, and A is the magnitude of the setpoint change at time zero,normalized to unity, M is a scale factor ranging from about 0.1 to about0.5, t is the instantaneous time in seconds, not to exceed about 1.5*τ,τ is a time constant ranging from about 0.1 to about 1.0 seconds, saidapparatus comprising a common outlet for said at least two materialsafter the same are combined, said common outlet being downstream fromsaid confluence region, and discharging said combined materials into acontainer that is removable from said apparatus.
 2. An apparatusaccording to claim 1, wherein τ is 1 and t ranges from 0 to about 0.5*τ.3. An apparatus according to claim 1, wherein τ is 0.5 and t ranges from0 to about 3*τ.
 4. An apparatus according to claim 1 wherein M is 0.5, τis 1 and t ranges from 0 to about 2.0*τ.
 5. An apparatus according toclaim 1 wherein M is 0.5, τ is 0.5 and t ranges from 0 to about 2*τ. 6.An apparatus according to claim 1 wherein M is 0.25, τ is 1 and t rangesfrom 0 to about 1.5*τ.
 7. An apparatus according to claim 1 wherein saidmajor material comprises a liquid.
 8. An apparatus according to claim 7comprising a pipe in fluid communication with said confluence regionthrough which pipe said major material flows.
 9. An apparatus accordingto claim 1 further comprising an inline mixer without a dynamicagitator, wherein said inline mixer is located at the confluence regionor downstream of the confluence region and permits continuous flow ofthe at least two materials through the portion of the apparatuscomprising said inline mixer.
 10. An apparatus according to claim 9wherein said inline mixer comprises an ultrasonic or cavitation typemixer.
 11. An apparatus according to claim 9 wherein said inline mixercomprises a static mixer.
 12. An apparatus according to claim 1 whereinsaid apparatus comprises at least one pump that is driven by a motor,and at least said major material is pumped into the confluence region bya pump.
 13. An apparatus according to claim 12 wherein said pumpcomprises a positive displacement pump.
 14. An apparatus according toclaim 12 wherein said motor comprises a servomotor.
 15. An apparatusaccording to claim 12 comprising a motor control loop wherein saidcomputer is in communication with said motor.
 16. An apparatus accordingto claim 15 wherein said motor comprises a servomotor, and said commandsignal is sent to said servomotor which accelerates or decelerates to aspecified rotational speed for the pump.
 17. An apparatus according toclaim 1 wherein said apparatus is free of flow control valves.